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POWhat data structure to use? (hash map vs. trie vs. ?)
 

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  1. POWhat data structure to use? (hash map vs. trie vs. ?)
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    <p>I have a C function that produces about 6 million unique arrays. These arrays always have 17 elements each, and each element is an integer from 0 to 16. I also have a slightly modified version of that function that will also produce about 6 million unique arrays of the same kind. My problem is that the second one produces about 45,000 results less than the first, and I'd like to see what these results are.</p> <p>So my approach is to simply store all the results of the second function (calculator tells me this should not take more than 400 mb which is fine to keep in-memory) and then look up the results of the first, printing out the ones that don't exist.</p> <p>Assuming the general approach makes sense (and if not, do tell), what I am looking for is an appropriate data structure (ideally with a good implementation in C) that can hold about 6 million unique permutations of </p> <pre><code>[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] </code></pre> <p>(or some transformation thereof) and then perform fast membership testing on them. As the title says, I do have some suspicions about which data structures may do the job, but I am not certain tries or hashmaps are the best choice for this.</p> <p>This is an algorithm to detect a flaw in another algorithm, not something that will be used in production. I am interested in doing this in a way that will be coded and return results relatively quickly in human terms, not necessarily shave milliseconds, so existence of easy to grok libraries that will do most of the job is definitely a plus.</p>
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    1. USAlexandros Marinos
    1. USAlexandros Marinos
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      1. POWhat data structure to use? (hash map vs. trie vs. ?)
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    1. COso basically you need to do `set(A) - set(B)`. A `set` implementation along with a `compare` routine could do the job.
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      1. USNick Dandoulakis
    2. COSince it's just a helper tool, non-production, does it have to be written in C? Other languages come with data structures included.
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      1. USSteve Jessop
    3. COWell the original algorithms are C, so it's convenient if I don't have to ship the data out to get the job done.
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      1. USAlexandros Marinos
 

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